get and set JSON quickly
json: object | array
object: '{' members? '}'
members: pair (',' pair)*
pair: string ':' value
array: '[' elements? ']'
elements: value (',' value)*
value: string
| number
| object
| array
| 'true'
| 'false'
| 'null'
string: '"' char* '"'
char: [^"\\\x00-\x1F]
| '\' escape
escape: ["\\/bfnrt]
| u [0-9A-Fa-f]{4}
number: '-'? (0 | [1-9][0-9]*) ('.' [0-9]+)? ([Ee] [+-]? [0-9]+)?